1. Field of the Invention
The present invention relates to the technique of evaluating the cleanliness of a substrate to be used for an electronic device and a cleaning technique, and more particularly, to a system for evaluating the amount of particles, a dip cleaning system, and a method of evaluating the amount of particles adhering to a substrate (hereinafter referred to simply as a xe2x80x9cparticle quantity evaluation methodxe2x80x9d), which enable high-precision quantitative evaluation of the amount of particles, i.e. the amount of dust particles, suspended in a liquid without use of a monitor substrate, which enable easy determination of the correlation between the amount of particles suspended in the liquid and the amount of particles adhering to the substrate which is an object of cleaning.
2. Background Art
Recent explosive proliferation of mobile communications equipment or multimedia equipment necessitates urgent measures to reduce a line width of a system LSI, a liquid crystal device, or a like device to be housed in such equipment, and to curtail device cost. Against such a technical backdrop, development of a low-cost technique for cleaning a substrate to be employed in a system LSI (a large-scale integrated circuit), a liquid crystal device, or a like device is indispensable. A dip cleaning system has been widely used for satisfying these requirements.
A dip cleaning system, for cleaning a substrate employed in an LSI, a liquid crystal device, or a like device, evaluates, in the course of a dip cleaning operation, the amount of particles, i.e. dust particles, originating from an apparatus, a chemical, or purified water, and evaluates the amount of particles adhering to a substrate which is an object of cleaning. The amount of dust originating from an apparatus or a substrate is usually evaluated on the basis of the amount of dust particle determined through cleaning of a monitor substrate. The number of particles suspended in a dip chemical treatment bath and the number of those suspended in a rinsing bath are evaluated by means of the technique of evaluating the amount of particles (background art of a first type), in which are directly sampled from a substrate treatment bath, i.e., a chemical treatment bath or rinsing bath.
Further, there has already been disclosed another technique for evaluating the amount of particles, in which, for example, the amount of particles suspended in a liquid stored in a chemical treatment bath is measured, to thereby evaluate the state of dust particle (background art of a second type).
There has also been disclosed still another technique for evaluating the amount of particles, in which, for example, the amount of particles suspended in a rinsing bath is measured (background art of a third type).
Background art of the first type suffers the following three problems: cost of a monitor substrate (a first problem); deterioration of productivity caused by treatment of a monitor substrate (a second problem); and comparatively unreliable evaluation, because the state of the surface of a monitor substrate differs from that of the surface of a substrate to be cleaned and the condition of particle adhesion differs according to the type of dust particles (a third problem).
Background art of the second type suffers the following three problems. A submerged-particle counter meets difficulty in returning to its initial state in a case where a large amount of dust particles have originated from a substrate to be cleaned (a first problem). A submerged-particle counter erroneously counts as particle bubbles of hydrogen peroxide (H2O2) which develop when a large amount of liquid hydrogen peroxide is present in a chemical (a second problem). Further, detection sensitivity is low in the case of a chemical of high concentration or at high temperature (a third problem).
Background art of the third type suffers the following two problems.
It is difficult to count the number of particles, because dust particles disperse immediately after a substrate is immersed in a rinsing bath, thus resulting in an extreme reduction in particle count (a first problem). A large measurement error stems from a difference in particle counts, because a stream present in a water cleaning bath is apt to change according to a flow rate of water supplied to the rinsing bath or the viscosity of a chemical used for treatment.
The present invention has been conceived in view of the previously-described drawbacks of the background art and is aimed at providing an system for evaluating the amount of particles, a dip cleaning system, and a method of evaluating the amount of particles adhering to a substrate, which enable high-precision quantitative evaluation of the amount of dust particles suspended in a liquid without use of a monitor substrate, which enable easy determination of the correlation between the amount of particles suspended in the liquid and the amount of particles adhering to the substrate which is an object of cleaning, and which enable low-cost and highly-reliable cleaning evaluation.
According to one aspect of the present invention, a system for evaluating the amount of particles adhering to a substrate is provided. The system comprises a residual liquid recovery pan for recovering a drop of residual liquid falling from the surface of the substrate. A pure water metering bath is provided for use in measuring particles suspended in pure water, as well as for effecting a standby state in which the bath is filled with a predetermined amount of pure water. A pure water supply source is provided for supplying pure water to the pure water metering bath. A residual liquid quantitative measurement bath is provided which drips a predetermined amount of sample liquid supplied from the residual liquid recovery pan into the pure water stored in the pure water metering bath. Further, a submerged-particle counter is provided for evaluating submerged particles and counting the number of submerged particles, through use of the solution which has been obtained by means of dropping a drop of sample liquid of given amount into pure water.
According to another aspect of the present invention, a dip cleaning system for evaluating the amount of particles adhering to a substrate is provided. The system comprises a first substrate treatment bath having a chemical treatment bath and/or a rinsing bath for dip cleaning purpose. Also provided is a second substrate treatment bath having a chemical treatment bath and/or a rinsing bath for dip cleaning purpose. Substrate transport means is provided for transporting the substrate from the first substrate treatment bath to the second substrate treatment bath. Further, a sub-system for evaluating the amount of particles adhering to the substrate as defined above is provided.
According to another aspect of the present invention, a method of evaluating an amount of particles adhering to a substrate includes the following steps. In a first and a second substrate steps, a substrate is chemical treated and/or a rinsed for dip cleaning purpose. In a substrate transportation step, the substrate is transported from the first substrate step to the second substrate step. In a residual liquid recovery step, a sample liquid is prepared by means of recovering a residual liquid dropping from the surface of the substrate during the course of the substrate being transported from the first substrate step to the second substrate step. In a pure water metering step, the bath is filled with a predetermined amount of pure water for effecting a measurement of the amount of particles suspended in pure water, as well as effecting a standby state. In a pure water supply step, pure water is supplied to the pure water metering step. In a residual liquid quantitative measurement step, the sample liquid of given amount determined by the residual liquid recovery step is dropped into the pure water prepared by the pure water metering step, and the measurement of the amount of particles adhering to a substrate is performed.
Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings.